System for storage and transportation of spent nuclear fuel

ABSTRACT

A concrete storage module ( 26 ) is adapted to slideably receive a cylindrical canister assembly ( 12 ) therein. Heat dissipation fins ( 62 ) and a tubular heat shield ( 96 ) are disposed within the module to help dissipate heat emitted from the nuclear fuel assemblies stored in the canister to air flowing through the module. The canister assembly ( 12 ) is composed of a basket assembly ( 70 ) constructed from multi-layer structural plates disposed in cross-cross or egg carton configuration. A single port tool ( 106 ) is provided for draining water from the canister ( 12 ) and replacing the drain water with make-up gas. The single port tool is mounted in the cover ( 100 ) of the canister and is in fluid flow communication with the interior of the canister.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 13/747,398,filed on Jan. 22, 2013, which claims the benefit of U.S. ProvisionalApplication No. 61/588,550, filed on Jan. 19, 2012, the disclosures ofwhich are hereby expressly incorporated by reference in their entiretyherein.

BACKGROUND

Part of the operation of a nuclear power plant is the removal anddisposal of irradiated nuclear fuel assemblies. Most early reactors wereoriginally built to store from three to five years' capacity ofirradiated fuel assemblies in a storage pool. From the storage pool, theirradiated fuel assemblies could be reprocessed or sent to long-termstorage. However, as a result of uncertainties in the federal policiesrelating to reprocessing of irradiated fuel and also in theestablishment of permanent irradiated fuel dumps, on-site irradiatedfuel storage facilities have been stressed to their capacity for storingthese irradiated fuel assemblies. To prevent the forced shutdown ofnuclear power plants as a result of the overcrowding of storage pools, anumber of near-term irradiated fuel storage concepts have been developedand/or utilized.

One such near-term concept in use is the dry storage of irradiated fuel.Nonetheless, early developments in irradiated fuel dry storage in theUnited States anticipated that this would be a short-term measure, withremoval of irradiated fuel to more permanent geologic storage requiredby Federal Law starting in 1998. As it became apparent that this wouldnot happen, and that interim dry storage would be a larger scale andlonger term effort, the following change occurred in the demands placedon dry storage systems.

As the initial inventory of low burnup, long cooled irradiated fuelresiding in pools was transferred to dry storage, and as power plantsincreased the enrichment and burnup of their fuel, the need to storefuel with ever greater residual decay heat has grown. The fuel gives offheat from the decay of the radioactive elements, and so the storagesystem must be able to keep the fuel cladding cool enough that it doesnot deteriorate during the dry storage period without the use of activecoolers such as fans. Early systems were developed with a capability forabout 24 kW of decay heat per system; current needs are in excess of 40kW.

Various structures have been developed to transport and store theirradiated fuel in secure canisters. One type of canister uses a latticestructure to form compartments to locate the fuel within the transportand storage canisters. The lattice structure is of “egg crate” designcomposed of interlocking transverse plates. However, existing baskets ofegg crate design have used very expensive materials. Such materialsinclude, for example, borated stainless steel, extruded profiles ofenriched boron aluminum and metal matrix composites. Thus, a need existsof constructing transport and storage canisters from lower cost and morecommon materials.

A system was developed for horizontal modular dry irradiated fuelstorage, as described in U.S. Pat. No. 4,780,269, the disclosure ofwhich is hereby expressly incorporated by reference. However, thereexists a need for improvements to that system. Embodiments of thepresent disclosure described herein are directed to fulfilling this andother needs.

SUMMARY

This summary introduces a selection of concepts in a simplified formthat are further described below in the Detailed Description. Thissummary is not intended to identify key features of the claimed subjectmatter, nor is it intended to be used as an aid in determining the scopeof the claimed subject matter.

A system for transportation and storage of spent nuclear fuel disclosedherein enhances the internal heat transfer during storage by theefficient use of high strength steel to construct the storage canisters,allowing more room for conductive material, aluminum or copper. Therejection of heat external to the fuel storage canister is enhanced bythe mechanical application of fins to the canister outside cylindricalsurface, or by the use of efficient and effective heat shields betweenthe canister and the concrete storage module, including designs thatincrease the surface area for convective heat rejection from the heatshields, in comparison to conventional heat shields.

The present disclosure employs lower cost materials employed in a novelway to construct an “egg crate” type transport and storage canisters forthe irradiated fuel. The plates of the egg crate structure employ lowalloy, high strength steel plates that encase aluminum and a thin sheetof a metallic base neutron absorbing material forming a functionallygraded structure where the steel provides structural stability, thealuminum conducts heat, and the neutron absorber prevents a neutronchain reaction.

In accordance with further aspects of the present disclosure, a canisterfor the transportation and storage of nuclear fuel assemblies includes abasket assembly receivable into a canister shell. The basket assemblyincludes a plurality of interlocking structural plates that are disposedin spaced parallel relationship to each other in a first direction, aswell as a plurality of structural plates disposed in a second directiontransverse to the first direction. The structural plates includingtransverse slots formed along the plates so that the slots of thestructural plates disposed in a first direction engage with the slots ofthe structural plates disposed in the second, transverse direction. Thestructural plates are composed of a plurality of separate layers,including outer layers composed of a structural material, at least oneinner layer composed of heat conducting material, and at least one innerlayer composed of neutron-absorbing material.

In accordance with further aspects of the present disclosure, the outerlayers of the structural plates are formed to encase the inner layers ofthe structural plates. In this regard, the margins of the outer layersextend over the edges of the inner layers and are joined to each other.

In a further aspect of the present disclosure, elongated locking keysextend along and engage with adjacent edge portions of adjacentstructural plates to lock the adjacent edge portions together and toalign the adjacent edge portions together. In this regard, grooves areformed along the edge portions of the structural plates. These groovesare sized to closely receive the locking key therein. Also, holes areformed in the structural plates, whereby the locking key passes throughthe holes of the structural plates that extend transversely to thelength of the locking keys.

In accordance with a further aspect of the present invention, transitionrails extend lengthwise of the canister at the outer perimeter of thebasket assembly to interconnect the structural plates. The transitionrails have an outer curvature in the direction transverse to the lengthof transition rails that correspond to the circumference of thecanister. In addition, the transition rails are at least partiallyhollow to receive a stiffening structure therein to enhance thestructural integrity and rigidity of the transition rails.

In accordance with a further aspect of the present disclosure, storagemodules for containing nuclear fuel assemblies in storage canistersinclude concrete bottom, side, and top walls. The modules are configuredfor air flow therethrough by natural convection to dissipate the heatemitted from the nuclear fuel assemblies. At least one heat transferstructure is disposed within the module and positioned to transfer heatfrom the canister to the air flowing through the module. In addition, atleast one heat shield is disposed in the module to shield the interiorof the module from heat emitted from the nuclear fuel assemblies.

In accordance with another aspect of the present disclosure, theconcrete top, bottom and side walls of the module are composed of amixture of concrete and metallic fibers serving to reinforce theconcrete.

In accordance with a further aspect of the present disclosure, the heattransfer structure includes fins that are disposed within the module fortransferring heat from the canister to the air flowing through themodule. The fins are placed into contact with the canister once thecanister is positioned within the module.

In accordance with a further aspect of the present disclosure, a heatshield structure and/or heat transfer structure includes barriers thatextend along one or more of the side walls, top wall and bottom wall ofthe module. Such barrier is spaced from the module walls to provide anair flow interface between the barrier and the module walls. The heatbarrier structure is selected from the group consisting of platestructures, corrugated wall structures, and tubular wall structures.

In accordance with another aspect of the present disclosure, a singleport tool is provided for the canister for fluid flow communication withthe interior of the canister for draining water from the canister andreplacing the draining water with make-up gas. The single port toolincludes a single opening formed in the canister and a shield pluginsertable within the opening. The single sport tool is in fluid flowcommunication with the interior of the canister and has a firstpassageway therethrough for receiving a drain tube for draining thewater from the canister, and a second opening therethrough for receivingmake-up gas and directing such make-up gas to the interior of thecanister.

In a further aspect of the present disclosure, the canister has ahousing and a cover, and a single port is formed in the cover of thecanister for reception of the single port tool.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisdisclosure will become more readily appreciated as the same becomebetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIGS. 1-4 are various views of a previously designed horizontal modulardry irradiated fuel storage system;

FIG. 5 is an isometric view of a horizontal dry storage module inaccordance with the present disclosure;

FIG. 6 is a view similar to FIG. 5, but with portions of the exterior ofthe module removed so that the interior structure of the module isvisible;

FIG. 7 is another view of a group of storage modules positioned side byside, with the module in the foreground showing portions removed so thatthe interior of the module is visible;

FIG. 8A is an enlarged fragmentary view of a heat transfer fin used in adry storage module;

FIG. 8B is a view similar to FIG. 8A of another heat transfer fin usedin the dry storage module;

FIG. 9 is an isometric view of a dry storage module with a top portionthereof removed;

FIG. 10 is a view similar to FIG. 9, but with heat shields as mountedwithin the dry storage module;

FIG. 11 is an isometric view of the basket portion of a storage canisterassembly, with portions broken away to illustrate the interiorconstruction of the basket portion;

FIG. 12 is an enlarged view of a plate used in forming the basketportion shown in FIG. 11;

FIG. 12A is an enlarged fragmentary view of how the plates that composethe basket portions are optionally interlocked together by offsettingthe edges of the interior sheets of the plate from the outer sheets ofthe plate so that adjacent plates can be locked together;

FIG. 13 is an enlarged fragmentary view of a plate used in forming thebasket portion;

FIG. 14 is an enlarged fragmentary view of the plate shown in FIG. 13with a cross hole formed therein;

FIG. 15 is a view similar to FIG. 14 but of a different cross holeconfiguration;

FIG. 16 is an alternative view of the plate shown in FIG. 13 showing themanner in which the exterior layers overlap each other;

FIG. 17 is a view similar to FIG. 16, showing a further alternative viewof the plate with the exterior layers joined together at a butt joint;

FIG. 18 is an enlarged fragmentary view of a basket plate showing oneway that the plate layers can be fastened together;

FIG. 19A is an enlarged fragmentary view of a transition railconfiguration placed along the outer perimeter of the basket assembly;

FIG. 19B is an enlarged fragmentary view of another transition railassembly;

FIG. 20 is a view of a canister assembly with basket assembly 70disposed therein;

FIG. 21 discloses a drain port tool for a canister assembly;

FIG. 22 is a further view of the drain port tool;

FIG. 23 shows the positioning of the drain port assembly relative to thecanister assembly;

FIG. 24 is a further view of the drain port tool;

FIG. 25 is an enlarged cross-sectional view of certain aspects of thedrain port assembly; and

FIG. 26 is an enlarged fragmentary view showing other aspects of thedrain port assembly.

DETAILED DESCRIPTION

A horizontal modular dry irradiated (e.g., spent) fuel storage systemwill first be described. With reference to FIGS. 1-4, a horizontalmodular dry irradiated fuel storage system 10 in accordance withembodiments of the present disclosure is presented. In addition,processes for storing irradiated fuel are described. As set forth ingreater detail below, the systems and processes described herein areimprovements to previous systems and processes described in U.S. Pat.No. 4,780,269 (as seen in FIGS. 1-4), the disclosure of which is herebyexpressly incorporated by reference.

Referring to FIG. 1, the system 10 uses a specially designed dryshielded canister assembly 12, which is shown in greater detail in FIGS.5-10, as described in greater detail below. The canister assembly 11 isinserted into a transfer cask 14. The transfer cask 14 and canisterassembly 11 can be placed by a crane 16 into an irradiated fuel storagepool 18 filled with water (see FIGS. 1 and 2). Irradiated fuel containedin fuel assemblies (see, e.g., fuel assembly 20) can be stored in thepool 18.

To remove the irradiated fuel from the pool 18, the fuel is placed inthe canister assembly 11, and appropriate seals and covers (as describedbelow) are affixed to the canister assembly 11 before the transfer cask14 is removed from the pool 18. Referring to FIG. 2, upon removal fromthe pool 18, water is forced out of both the canister assembly 11 andthe transfer cask 14 with a pressurized gas being applied throughselected ports of the canister assembly and cask. The canister assembly11 is further dried by using a vacuum pump to evacuate the residualwater from the canister assembly 11. After evacuation of the canisterassembly 11, helium gas is pumped into the canister assembly 11. As thetransfer cask 14 (containing the canister assembly 11 and irradiationfuel assemblies 20) is removed from the pool 18, appropriate radiationshielding is provided for the contained irradiated fuel assemblies bythe shielded end plugs of the canister assembly 11 and the transfer cask14.

Referring now to FIG. 3, the transfer cask 14 can be loaded into ahorizontal position onto a transfer trailer 22 having a speciallydesigned skid 24. The skid 24 allows the transfer cask 14 to be moved inthree dimensions to permit alignment of the cask 14 with a horizontalstorage module 25, which can be seen in FIG. 4, for dry storage of thecanister assembly 11.

Referring to FIG. 4, the cask 14 is aligned with a port 28 in the drystorage module 25 to extract the canister assembly 11 from the transfercask 14 for storage in the horizontal storage module 25. In theillustrated embodiment, a hydraulic ram 30 is at least partiallyinsertable through a second port 32 at the opposite end of the drystorage module 26 to extract the canister assembly 11 from the transfercask 14 for storage in the horizontal storage module 25. Alternatively,a winch (not shown) or another extraction device could be used in placeof ram 30 to extract the canister assembly 11 from the transfer cask 14.It should further be appreciated that the reverse operation of pushingthe canister assembly 11 into the dry storage module 25 can also beaccomplished.

Referring to FIGS. 5-10, detailed views of an improved horizontal drystorage module 26 are provided. The horizontal dry storage module 26includes a housing 40 having a top section 41. The housing 40 is inblock or rectilinear form and is preferably constructed from reinforcedconcrete, which may be positioned on a load-bearing foundation 42 (see,e.g., FIG. 4). In a previous design, the housing 40 was formed fromconcrete reinforced with rebar. However, in the improved design, thehousing 40 is reinforced with metal fiber, for example, steel fiber, toincrease blast and earthquake resistance and provide long-term crackresistance. The metal fiber also reduces shrinkage and cracking of theconcrete in the short term, thereby decreasing water incursion and alsoincreasing spalling resistance in the long term. In sum, the use ofsteel or other comparable fibers to reinforce the concrete increases thetoughness, tensile strength, density, and dynamic strength of theconcrete. It should be appreciated that vertical storage modules orother storage modules (not shown), having housings that are reinforcedwith metal fiber, for example, steel fiber, are also within the scope ofthe present disclosure. Also, it is to be appreciated that the use ofmetal fiber to reinforce the concrete can be used in lieu of or inaddition to primary and secondary rebars used in standard concreteconstruction. Also, it is to be appreciated that other high-strengthfibers can be used in place of or in addition to metal fibers, such asfiberglass fibers, glass fibers, or carbon fibers.

The housing 40 includes an inlet 44 at one end and an interior volume 46designed for receiving and containing a canister assembly 12. Embeddedin housing 40 is an underlying support assembly 48 to support thecanister assembly 12 when it is fully inserted into housing 40. Thesupport assembly 48 may also be configured to allow the canisterassembly 12 to slide easily in and out of the housing 40. As shown inFIGS. 5-7, the support assembly includes parallel slide rail assemblies49 extending along the housing in the lower portion of the interiorvolume 46. The slide rails may include slide strips composed of materialthat is galvonically compatible with the canister 12 and durable underthe radiation level and temperature within interior volume 46. The sliderails themselves may be composed of such material or a coating orsurface treatment may be applied to the slide rails.

The housing 40 includes a closure device 50 to cover the inlet 44. Theclosure device 50 may be constructed from steel and/or concrete and/orother appropriate radiation protection media. The closure deviceincludes an inner, round-shaped cover plug 54 and an outer hat plate 52that is sized to overlap the front wall of the housing surrounding theinlet 44. The wet plug 54 closely fits within inlet 44. As can be seenin FIGS. 5 and 6, the closure device 50 can be appropriately positionedin place when a canister assembly 12 is disposed in the module 26.

Referring to FIG. 7, the housing 40 may be designed and configured toallow similar housings 40 to be placed adjacent other housings, whichmay be interlocked therewith. Therefore, several housings can be stackedtogether in series to provide additional shielding to minimize radiationleakage.

Referring to FIGS. 6 and 7, the horizontal dry storage module 26 mayinclude a heat dissipation assembly 60. In the illustrated embodiment,the heat dissipation assembly 60 includes a plurality of curved,relatively thin fins 62 spaced along the module 26. The fins 62 areeither lowered onto, or clamped like a clamshell onto, the outer surfaceof the canister assembly 12 after the assembly is installed in themodule 26. The fins 62 enhance convective heat transfer from thecanister surface to the air flowing through the module 26.

As can be seen in FIG. 6, in one embodiment of the present disclosure,the heat dissipation assembly 60 consists of a series of curved finsthat are mounted to the underside of a longitudinal bar 64. The bar inturn depends from a series of rods 66 that extend through the topsection 41 of the housing 40 to terminate at threaded upper end portionsthat engage threaded fasteners 66. The heat dissipation assembly isinitially retracted, positioned at the top or roof of the module 26 byrotation of fasteners 66 on rods 64. Once the canister assembly 12 hasbeen inserted within module 26, the fasteners 46 are used to lower thebar 64 and associated fins 62 down onto the upper surface of thecanister.

Although in FIG. 6, the upper threaded ends of bars 64 are shown asprotruding above the upper surface of housing top section 41, insteadthe upper end of the rods 64, as well as threaded fastener 66, may bedisposed below the top surface of top section 41. In this regard, wellsor sockets may be formed in the upper surface of the top section 41, sothat once the assembly 60 has been deployed downwardly against canisterassembly 12, the wells or sockets can be plugged or otherwise securelyclosed off.

Rather than being constructed as shown in FIGS. 6 and 7, the heatdissipation assembly 60 may be constructed in two separate sections,with each section hinged to the interior of housing 40, for example,along the lower side portions of the housing. Once canister assembly 12has been installed in the module 26, such hinged fin sections could berotated to bear against the exterior of canister assembly 12 in aclamshell-like arrangement.

Rather than constructing the heat dissipation assembly 60 as a movableunit, the assembly can be formed from stationary fins, for example, fins62′ or 62″ shown in FIGS. 8A and 8B. Flexible, heat transmittinginterfaces 68 or 69 are provided along the edges of fins 62′ and 62″that face the canister 12. In FIG. 8A, the interface 64 is in the formof a hollow, bulbous shape that can be deformed when the canister 12 isslid into module 26. As shown in FIG. 8A, the interface forms an oval orelliptical shape when pressed against the exterior of canister assembly12. In FIG. 8B, the interface is in the form of a flexible lip assembly69 that flexes and presses against the exterior of canister assembly 12when the canister is slid into place within module 26. As noted above,both of these interfaces are highly heat conductive. The fins 62 may beconstructed from aluminum or any other suitable metal or non-metalmaterial designed for heat conduction and collection.

Referring to FIG. 9, one or more access ports 92 may be provided in thefront wall of the module 26 and on plate 50 for inspection of the module26 interior space 46 and the surface of the canister assembly 12 duringlong term service, off-normal events, etc. As seen in FIG. 9, the ports92 maybe closed off by suitable shielding plugs 94. The ports 92 may bevarious configurations and at various locations on the front wall andplate 52.

Referring to FIG. 10, tubular heat shields 96 are positioned in theinterior space 46 of the module to increase the surface area fortransferring radiant heat from the canister 12 the air flowing throughthe module 26 relative to if the shield was composed of a flat plate,while at the same time protecting the housing 40 (which is made fromreinforced concrete) from excessive heat. The heat shields 96 can becomposed of standard square or rectangular cross-sectional metallictubes, for example, steel or aluminum, or other heat conductingmaterial. The individual tubes can be secured adjacent to each other bywelding, mechanical fastening, or other expedient means. A mechanicalfastener could include rods that extend transversely through the tubes.Alternatively, transverse tie rods could extend transversely over theexterior of the tubes, with the tie rods welded or otherwise fastened tothe tubes. Also, the surface of the shields 96 that face canister 12 canbe treated to increase their radiant emissivity, and thus increase theirability to absorb or otherwise capture infrared heat from canisterassembly 12. The tubular shields 96 are mounted to the interior sidewalls and top walls of the housing 40 by suitable brackets thereby tospace the shields from the adjacent walls of the housing 40. Thisprovides a relatively cool layer of air between the shield and theconcrete wall of the canister assembly 12 thereby to protect theconcrete from excessive heat, which of course can weaken the structuralintegrity of the concrete.

Rather than using heat shields 96 of tubular construction, the heatshields can be of other constructions, including one or moresubstantially flat plates or a plate of corrugated construction, withthe corrugation taking many cross-sectional shapes, such assemi-circular, rectilinear, triangular, etc. Also of course thesealternative constructions for heat shields 96 can be composed of variousmaterials having different levels of radiant heat absorption and heatconduction.

As noted above, the heat shields 96 enhance the overall heat rejectioncapability of canister assembly 12 by increasing the surface area forheat rejection. The heat shield is heated both by radiation and by airflowing from the canister to the near surface of the shield by naturalconvention. The tubular or corrugated heat shields increase the surfacearea compared to a flat heat shield, thus making the heat shield moreeffective for transferring heat to the cooler air which flows inside thetubes composing the shields 96, as well as the air that flows betweenthe tubes and concrete wall of the housing 40. This directly increasesthe surface area available for transferring heat away from the canister12. Also, the tubes that compose shield 96 provide two separateshielding surfaces, one facing the canister and one facing the concretewall, thereby increasing the ability of the shield 96 to serve as a heatbarrier and protecting the concrete walls of the housing 40 from beingoverheated.

Referring to FIG. 11, a basket assembly 70 for being disposed in thecanister 12 to hold fuel assemblies 20 will now be described in greaterdetail. The basket assembly 70 is in the form of a rack positionedinternal to the canister assembly 12 for locating and supporting thefuel assemblies during storage and transportation.

Referring to FIGS. 11, 12 and 12A, the basket assembly 70 has astructure composed of functionally graded plates 72 that interlock in acriss-cross or “egg crate” matrix to define a plurality of tubes 74(square or rectilinear in cross-section) for receiving individual fuelassemblies. The plates 72 are formed in a plurality of layers forstructure, heat transfer, and neutron absorption as described more fullybelow.

Referring specifically to FIGS. 13-17, the plates 72 may include amulti-layer structure. As a non-limiting example, the plates 72 may havea four-layer structure including first and second steel outer layers 80and 82, a heat conductor interior layer 84, and a neutron absorber layer86. As a non-limiting example, the steel outer layers 80 and 82 may be ahigh strength, low alloy steel, a high-strength steel, a carbon steel,stainless steel or other comparable materials. As a non-limitingexample, the heat conductor layer 84 may be manufactured from aluminumor copper or other highly heat conductive metal or material. As anon-limiting example, the neutron absorber layer 86 may be manufacturedfrom a material whether metallic, ceramic or a composite, that containsan element that absorbs thermal neutrons. Such materials include, butare not limited to, boron, cadmium, and gadolinium. As such, the layer86 may be composed of a metal matrix composition, such as a composite offine boron carbide particles in an aluminum or aluminum alloy matrix.The aluminum matrix may consist of 99% pure aluminum.

Also, it is to be understood that the heat conducting function andneutron absorption function can be combined into a single layer ofmaterial that can both conduct heat and absorb neutrons. Such materialscan include but cannot be limited to, aluminum or copper with embeddedparticles of boron carbide.

The plates 72 may include flush fasteners 76 for securing the layers ofthe plate to each other in face-to-face relationship, see FIG. 18.Suitable fasteners 76 may include, for example, threaded fasteners,rivets or welded joins. In the illustrated embodiments of FIGS. 14 and15, holes 88 for receiving fasteners 76 may be formed by punching,drilling or other methods in the plates 72.

Referring to FIG. 18, an exemplary threaded torque limiting fastener 76,which is flush with the exterior surfaces of the plate 72, on bothsides, is shown. The fastener has a bolt section 76A composed of abeveled head 76B and a shank 76C. The threaded section 76D engages withthe interior of a threaded nut 76E, which also has a beveled head 76F.The beveled heads 76B and 76F bottom against beveled counter boresformed in the layers 80 and 82. Then the fastener 76 is fully engagedthe heads 76B and 76F of the fastener are flush with or beneath theouter surfaces of plate layers 80 and 82.

In one embodiment of the present disclosure, the layers of the plates 72are furnace-brazed together. Exemplary constructions for thefurnace-blazed plates 72 are shown in FIGS. 16 and 17. Referring to FIG.16, the edges of layers 80 and 82 are bent around and over each other inoverlapping fashion at 89A for adding buckling resistance. Referring toFIG. 17, the bent edges of layers 80 and 82 are welded to each otheralong the butt seam 89B to form a rigid tubular structure with the othercomponents (layers 84 and 86) encased inside the tube.

In one embodiment of the present disclosure, the plates 72 may include ablack oxide coating on one or both steel layers 80 and 82 to provideimproved radiation heat transfer from the fuel assemblies (not shown) tothe basket assembly 70. In addition, the outer surfaces of the plates 72may further include a hydrophobic silicon dioxide coating to improvewater shedding and thereby reduce drying time.

The plates 72 can be constructed in different thicknesses and widths.The thicknesses of the plates can depend on various factors, includingthe weight of the fuel being transported and stored, the amount of heatconduction desired by layer 84 as well as the level of neutronabsorption desired for a layer 86.

The widths of the plate 72 can depend on the overall length of thebasket assembly 70, since such length is composed of plates 72 stackedlengthwise upon each other. As a non-limiting example, the plate 70 canrange in width from about 10 inches to about 16 inches or even wider.

The basket assembly 70 shown in FIG. 11 is composed of plates 72 thatare fitted together in criss-cross or “egg crate” manner. Also referringto FIGS. 11, 12, and 12A, the plates 72 have transverse slots 73 thatextend a quarter of the way across the width of the plate. As aconsequence, when the plates 72 are fitted together so that the slots 73of the criss-crossing plates engage each other, adjacent plates in thevertical direction mate edgewise against each other. In this manner, aplurality of vertical cells 74 are formed for the full height of thebasket assembly 70. Ideally, each of the cells 74 are only slightlylarger in cross-section than the nuclear fuel assemblies that arecontained or stored in the basket assembly 70.

As will be appreciated at the very top and bottom of the basket assembly70, the plates 72 are only half as wide as throughout the remainingheight of the basket assembly. Moreover, the slots 73 in the upper mostand lower most plates 72 extend half-way through the width of suchplates. As a consequence, the bottom edges of all the lower mostcriss-crossing plates are on the same plane. Likewise, at the top ofbasket assembly 70, the upper edges of the upper most criss-crossingplates 72 are also of the same elevation.

Referring specifically to FIG. 12A, as an optional construction ofbasket assembly 70, the longitudinal edges of the plates 72 are formedwith a groove 74 extending along the upper and lower edges of each ofthe plates 72. The groove is sized to receive a close fitting bar or key75 that is sized to be very closely receivable within the opposinggrooves 74 of adjacent plates 72. The rod or bar 74 passes throughopenings 75A formed in the plates 72 in alignment with the two opposingslots 73 of a plate 72 and half way between such opposing slots 73. Aswill be appreciated by the foregoing construction, the bars 72 lock theadjacent edge portions of adjacent plates 72 together to form a veryrigid construction for the basket assembly 70. The width of the groove74 can be the thickness of the plate inner layers 84 and 86. As such,the groove 74 is formed by extending the outer layers 80 and 82 beyondthe edges of the inner layers 84 and 86.

Referring to FIGS. 19A and 19B, transition rails 90 and 92 may bedesigned for placement along the outer perimeter of the basket assembly70 to help form the cylindrical outer structural shape of the basketassembly 90 when received in a canister assembly 12, see FIG. 11. Inthat regard, the rails 90 and 92 may be configured as cast or extrudedaluminum alloy rails to provide strength and creep resistance to thebasket assembly under long term exposure to the fuel assemblies at hightemperature. The transition rail 90, shown in FIG. 19A, is generallytriangular in cross section and having an outer curved side or surface91 of a transverse curvature corresponding to the overall outercurvature of basket assembly 70, shown in FIG. 11. To provide structuralintegrity to the rail 90, an interior bracket or brace 91A may beutilized. As illustrated in FIG. 19A, the brace 91A is shown in the formof a rectangular tubular member. Through-holes 91B are formed in brace91A in alignment with corresponding holes formed in the adjacent wall91C of transition rail 90 through which appropriate fasteners may beengaged. Such fasteners, shown in FIG. 11, also extend through theadjacent plates 72 of the basket assembly. It will be appreciated thatthis construction aids in creating the basket 70 as a very rigidstructure. Other than the cross sectional area taken out by the walls ofbrace 91A, the interior of transition rail 90 is hollow to minimize theweight of the rail and also to allow air to pass therethrough to aid inheat dissipation. As shown in FIG. 11, two sets of rails 90 are used ineach quadrant of the basket 70.

Two sets of transition rails 92 are also used in each quadrant of basket70. The transition rails 92 are thinner in cross section than rails 90,but do include a curved outer surface 93 of a transverse curvaturecorresponding to the outer diameter of basket 70. The rails 92 include alongitudinal opening 93A for reception of a reinforcing tube 93Bextending lengthwise through the rail. The reinforcing tube 93B isprovided to help stiffen the rail 92. Of course, reinforcing members ofother shapes can be used in place of tube 93B. Also, through cavities93C and D extend lengthwise through the rail 92. These cavities helpreduce the weight of the transition rail without significantly reducingthe structural integrity of the rail. Moreover, air is able to flowthrough the cavities 93C and 93D, extending the length of the transitionrail 92, thereby to help dissipate the heat generated from the fuelassemblies 20 disposed within the basket 70. The transition rail 92 issecured to adjacent plates 82 by fasteners 93E that extend throughaligned openings formed in the plate 72 and in rails 92, see FIG. 11.Also, when in place, groove 93F formed in the interior wall section oftransition rail 92 mate with the end portions of plates 72 that protrudebeyond the furthest outward cross plate 72, for instance, as shown inFIG. 11. This interlocking relationship with the ends of the plate 72also add to the rigidity of the construction of the basket 70.

Returning to FIG. 7, a canister assembly 12 is shown in a module 26.Referring now to the cross-sectional view of FIG. 20, the canisterassembly 12 is a substantially cylindrical container having an outershell 96 and a distal end 98 and is designed for containing the basketassembly 70 for storage and transportation of fuel. The canisterassembly 12 further includes a closure assembly 100 at its proximal end,as described in greater detail below. Most lightweight reactor fuel isin the range of about 146 to 201 inches in length. As such, the canisterassembly 12 is constructed at a length corresponding to the length ofthe reactor fuel. As discussed above with reference to FIG. 2, thecanister assembly 12 must be dried after it has been removed from thepool 18. In that regard, water must drained from both the canisterassembly 12 and the transfer cask 14 that surrounds the canisterassembly 12. See, for example, FIG. 2.

Referring to FIGS. 21-23, in accordance with one embodiment of thepresent disclosure, a canister assembly 12 has been designed with an endclosure assembly 100 that includes a shield plug 102 and an inner topcover plate 104 outward of the shield plug and a single integrated ventand drain port tool 106. The shield plug and inner top cover plate 104close off the proximal end of outer shell 96. The shield plug isrelatively thin and can be composed of material to contain the nuclearfuel assemblies within the canister assembly. Such materials mayinclude, for example, steel, lead, tungsten and depleted uranium. Theintegrated port tool 106 has the capability to drain water and alsoprovide an inert gas (e.g., helium) cover for fuel assemblies 20.Therefore, the canister assembly 12 includes means for controlling thegas that enters the interior of the canister assembly 12 while the wateris being pumped out.

The port tool 106 of FIGS. 21-23 may be configured as an adapter toreplace separate drain and vent ports that are conventionally used inexisting canister assemblies. In the illustrated embodiment of FIGS.21-23, the port tool 106 generally includes an adaptor body 108extending through inner top cover plate 104 and into the shield plug102. The port assembly 106 also includes a vent 110 in communicationwith the interior of canister assembly 12 for gas supply into thecanister assembly and a water removal tube 112, extending through acentral passageway formed in body 108, for water to exit from thecanister assembly 12. The vent 110 is composed of an outer nipple 111that is connected to a vent passageway 114 formed in the adapter body108. In FIG. 22, the vent 110 is shown as consisting of a tube 111C thatextends through a vent passageway extending through the adapter body108. In use, gas is supplied to the vent 110. Water may be pumped viatube 112 or forced out at tube 112 by gas pressure applied at vent 110.

The adaptor body 108 of the port tool 106 is attachable to the inner topcover plate 104 by any suitable means, including threading, a bayonetlock, screw flange, or quick thread from the top. An exemplary threadedattachment 114 is shown in the illustrated embodiment of FIG. 22. Inaddition, a plurality of elastomeric x-rings 115A and o-rings 115Bensure a tight seal between the port assembly 106 and the inner topcover plate 104. O-rings 115C also are disposed between water removaltube 112 and the passageway extending through adaptor body 108.

A port is formed by a cup 116 welded under the inner top cover plate104. The cup 116 has a center hole 118 for receiving the water removaltube 112. The hole 118 has a diameter that is sized slightly larger thanthe outer diameter of the water removal tube 112 to provide an annularflow path for the backfill gas entering from vent 110. The water removaltube 112 may be a removable drain tube, that extends the length of thecanister assembly 112.

A top view of the port tool 106 in the canister assembly 112 can be seenin FIG. 23. The port is located at the perimeter of the basket, as canbe seen in hidden view through outer cover 104, as viewed from the topof FIG. 23.

The port and port tool 106 provide advantages over existing drain ports.These advantages include reduced manufacturing costs by the ability toprovide a deep port in a relatively thin lower plate rather than thethick cover plates or vent and drain block commonly used. Moreover, theport assembly of the present disclosure reduces operation time and doseby reducing the number of ports that need to be closed (from two toone), and by the use of the thick adaptor body 108 that acts as aradiation shield. By sliding the tube 112 in the adaptor body 108, thegap between the bottom of the tube and the bottom end of the canistercan be adjusted to optimize the removal of aspirated droplets, thusoptimizing the removal of all water from the canister assembly 12. Inaddition, because the tube 112 is entirely removed during vacuum dryingas shown in FIG. 24, the large opening improves the conductance forvacuum drying, which also reduces drying time, optimizing the removal ofall water from the canister assembly 12. In addition, the port assembly106 improves the conductance for vacuum drying, which also reducesdrying time.

Fuel loading operations will now be described. After fuel has beenloaded into the canister assembly 12 (see, for example, FIG. 1), theshield plug 102 (shown in FIGS. 21 and 22) is installed while thecanister assembly 12 and surrounding cask assembly 14 still remainsunder water. Rotational orientation of the canister assembly within thecast assembly is controlled by a key on the side wall of the canisterassembly 12. The shield plug 102 does not engage a drain tube.

A short hose is inserted into the canister assembly 112 to drain thewater as needed from the canister assembly 12 and the inner top 104cover is installed after the cask assembly 14 has been set down. Theinner top cover 104 is then welded, and the drain tube 112 and port tool106 are then installed.

After the drain tube 112 and port tool 106 have been installed, thedrain tube 112 is pushed to the bottom of the canister 112, then raisedup about ⅜ inch (10 mm) and secured with a locking collar, not shown.The inert gas (e.g., helium) supply is attached to the vent tube 110,and the water pump is attached to the water drain tube 112. Gas flow andwater pumping is initiated. In that regard, the gas pressure under theport assembly 106 should be slightly positive.

At the first sign of cavitation (air in the water pump), the drain tube112 is lowered and pumping is continued until water is no longer beingpumped out. The water pump is them disconnected from the drain tube 112and a vacuum pump with a water trap is attached to the drain tube 112.

Gas continues to be supplied through the vent tube 110 while gas andwater are removed from the canister assembly 12 by the vacuum pump. Thedrain tube 112 can be raised and lowered slightly during vacuuming tofind the ideal gap between the drain tube 112 and the bottom of thecanister assembly 12.

Referring now to FIG. 26, another embodiment of a port assembly 306 fora canister assembly 12 is shown. In the embodiment of FIG. 26, the portassembly 306 includes a permanent tube 322 in the canister assembly 12with a cup 340. A short removable tube 312 is connectable to thepermanent tube 322 for drain operation, and removed for vacuum drying.The tube section 312 is comparable to the upper end of tube 112,discussed above. The permanent tube 322 in the canister assembly 12connects with the threaded cup 340. Alternatively, the cup can bepermanently affixed to tube section 312. The cup 340 can move enough toself align. The permanent tube 322 can also move up and down, but doesnot rotate and it does not engage the shield plug or any other lidcomponent other than the tube 312 that is part of the port tool 106.

INDUSTRIAL APPLICABILITY

The system described herein can be used to provide a solution to theproblem of storage of irradiated fuel assemblies. The system isparticularly appropriate for use as an interim solution to theirradiated fuel storage problem until provided by governmentalauthorities. Accordingly, the present disclosure provides for arelatively inexpensive temporary storage facility for irradiated fuelassemblies. The system uses and reuses existing casks to transfercanisters with the irradiated fuel assemblies to modules 26 fornear-term storage. Further there is no requirement for a lifting craneat the storage site, because horizontal loading and unloading isenabled. In addition, the fuel canisters 12 can be comprised of athin-walled material, because the canister is always protected either bythe module 26 or by the transfer cask 14.

In view of the use of existing technology and equipment, investment inhorizontal dry storage module 26 can be spread over a number of years,because the modules 26 need only be fabricated and positioned as theyare required. Also, when appropriate long-term solutions for the storageof irradiated fuel assemblies have been reached, the modules 26 can beeasily deactivated and the assemblies still inside the canisters can betransported to the permanent storage facility.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the disclosure.

The embodiments of the disclosure in which an exclusive property orprivilege is claimed are defined as follows:
 1. A storage module forstoring canisters containing nuclear fuel assemblies, said storagemodule comprising: concrete bottom, side and top walls; said moduleconfigured for airflow through the module by natural convection todissipate the heat emitted from the nuclear fuel assemblies; at leastone heat transfer structure disposed within the module and positioned totransfer heat from the canister to the air flowing through the module;and at least one heat shield disposed in the module to shield theinterior of the module from the heat emitted from the nuclear fuelassemblies.
 2. The canister storing module of claim 1, wherein theconcrete bottom, top and side walls of the module are composed of amixture of concrete and metallic fibers serving to reinforce theconcrete.
 3. The canister storing module according to claim 2, whereinthe metallic fibers are selected from the group consisting of steelfibers, glass fibers, and carbon fibers.
 4. The canister storing moduleaccording to claim 1, wherein said heat transfer structure comprisesfins disposed within the module for transferring heat from the canisterto the air flowing through the module.
 5. The canister storing moduleaccording to claim 4, wherein said heat transfer structure furthercomprising a mounting structure for mounting the fins within the moduleto provide clearance relative to the storage canister when the storagecanister is being inserted within the module and then placing the finsagainst the storage canister once the storage canister is placed withinthe module.
 6. The canister storing module according to claim 5, whereinthe mounting structure hingedly mounts the fins within the module torotate into engagement with the canister once the canister has beenplaced within the module.
 7. The canister storing module according toclaim 5, wherein the mounting structure for the fins mounts the fins atan initial location spaced from the storage canister when the storagecanister is placed within the module and then advancing the fins to bearagainst the storage canister once the storage canister has been placedwithin the module.
 8. The canister storing module according to claim 4,wherein the fins have a deformable inner face portion that pressesagainst the canister as the canister is inserted within the storagemodule and continue pressing against the canister once the canister isin place within the storage module.
 9. The canister storing moduleaccording to claim 1, wherein said heat shield structure and/or heattransfer structure includes a barrier structure extending along one ormore of the side walls, top wall, and bottom wall of the module andmounted to the module to be spaced from the corresponding wall of themodule to serve as an impediment to the heat emitted from the storagecanister to reach the walls of the module and to transfer the heat fromthe storage canister to the air flowing through the module.
 10. Thecanister storing module according to claim 9, wherein said heat barrierstructure is a structure selected from the group consisting of the platestructure, a corrugated wall structure, and a tubular wall structure.11. The canister storing module according to claim 1, wherein thesurface of the heat barrier structure facing the canister is treatedwith a high-emissivity surface treatment or coating to increase theradiative heat transfer from the canister surface to the barrierstructure.